1. Field
Aspects of the present disclosure relate generally to the field of wireless communication, and more particularly, to methods and apparatus for controlling rejection of downlink (DL) Transmit Power Control (TPC) commands in a windup mode.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks.
In UMTS, user equipment's (UE's) transmit power may be controlled by base station (e.g., NodeB) using Downlink (DL) Transmit Power Control (TPC) commands transmitted on a downlink (DL) Dedicated Physical Control Channel (DPCCH). Generally, DLTPC command includes either 0 (power down) or 1 (power up) bits. UE decodes the DLTPC commands and adjusts its transmit power accordingly. In some instances, a large sequence of unreliable DLTPC down commands (0 bits) may cause sudden drop in UE's transmit automatic gain control (TxAGC) to a very low level. Sometimes UE recovers its TxAGC by itself and sometimes it does not, which may cause radio link failure. It has been observed, that this odd behavior, i.e., a large sequence of DLTPC down commands, may occur when the UE is in a windup mode.
Windup mode is a power control behavior in which signal-to-interference ratio estimate (SIRE) of the received signals by the UE is too low to maintain the required Block Error Rate (BLER) of the DL channel transmissions and increasing the NodeB's transmit power does not improve the received signals at the UE. This situation is illustrated in FIG. 1. As shown, windup mode may occur when, for example, UE passes large buildings, which may cause shadowing effect that can makes the NodeB's DL signals weak in that area. Because of the shadowing, increasing NodeB's transmit power does not improve the DL channel SIRE, wastes NodeB's power and causes interference to other UEs. The TPC Down commands (0 bits) are likely caused by the TPC command decoding errors and, therefore, should not have been all rejected given the average DL channel SIRE is still higher than the rejection threshold for Down commands for multiple TPC groups. Accordingly, there is a need to solve this DLTPC decoding issue when the UE is in the windup mode.